With an IP network system for transmitting data by use of a conventional IP (an Internet Protocol), a router duplicates a packet to be transmitted to generate a plurality of duplicate packets, and the plurality of the duplicate packets are transferred to a destination via a plurality of routes, thereby enabling the packet from a transmission source to reach the destination even if a trouble occurs to any of the routes.
The related art associated with the conventional IP network system includes the following.
[Patent Document 1] JP 2005-218112A
FIG. 31 is a configuration block diagram showing an example of a conventional IP network system. In FIG. 31, hosts 1, 4 each have a communication function for transmitting a packet by use of the conventional IP. Routers 2, 3 each have a communication function, and a routing function for selecting a route through which a packet is to be transmitted. The host 1, and the router 2 are mutually connected to each other, and the routers 2, 3 are connected to each other through the intermediary of a complex network NW100 comprised of a plurality of repeaters such as switches, routers, and so forth. Further, the router 3, and the host 4 are mutually connected to each other.
Further, FIG. 31 shows a packet communication DF100 flow whereby the router 2 transmits a packet to the router 3 via a route A inside the network NW100, and a packet communication DF101 flow whereby the router 2 transmits a packet to the router 3 via a route B inside the network NW100.
FIG. 32 is a flow chart for describing an operation of the IP network system. First, in step S101, the host 1 generates a packet whose final destination is the host 4, containing data such as measured data, and so forth, transmitting the packet to the router 2.
In step S102, the router 2 duplicates the packet received from the host 1. In the case of transferring the packet via two routes, for example, the routes A, B, as shown in FIG. 31, the router 2 duplicates two packets (for example, a duplicate packet PKT-A, and a duplicate packet PKT-B) out of the packet received from the host 1.
In step S103, the router 1 transfers the two duplicate packets to the router 3 through the intermediary of the network NW100 on the basis of preset routing-information.
The router 2 transfers the duplicate packet PKT-A along the route A to the router 3, as shown in, for example, the packet communication DF100 flow of FIG. 31, and the duplicate packet PKT-B along the route B to the router 3, as shown in the packet communication DF101 flow.
Then, the router 3 transfers either of the packets received from the router 2 (for example, the duplicate packet PKT-A, or the duplicate packet PKT-B) to the host 4.
Thus, the router duplicates the packet received from the transmission source, and transfers those duplicate packets via a plurality of the routes, respectively, so that even if packet communication is disabled due to a trouble occurring to any of the routes, the duplicate packet is transferred via another route, thereby enabling the packet from the host at the transmission source to reach the host at destination.
Now, there can be the case where the IP network system described as above ends up having a configuration wherein the respective routes each pass through the same router (including, for example, the case where both the routes A, B inevitably pass through a router X), depending on routing executed by the respective routers. In such a case, there has been encountered the case where packet communication is disabled along all the routes if a trouble occurs to the router X.
In order to preempt the inability to execute packet communication along all the routes upon occurrence of a trouble at a certain router, there is the necessity of setting such that the respective routes each do not pass through the same router. Accordingly, setting of routing by all the routers has been precisely pre-designed, and subsequently, control•setting of a routing table for all the routers has been in practice.
However, with a method for setting routing for all the routers in order to prevent the respective routes from passing through the same router, a problem is encountered in that routing for all the routers must be set every time a system configuration is changed. Furthermore, such a method as described has another problem in that since the routing table for all the routers must be controlled, much time is required in maintenance.